Cardiac Anatomical and Electrical Axes: Proposed Definitions and Interplay

The influence of heart size, position and orientation within the torso on ECG morphology is well-established.Yet, there remains a gap in quantifying and accounting for the impact of this relationship on the ECG biomarkers extracted, presenting an opportunity for tailoring clinical ranges, thus, improving the reliability and robustness of diagnosis and prognosis of electrophysiological disorders.In this context, the aims of this study are (1) to propose a standardised and robust definition of the electrical and anatomical axes, and (2) to describe their relationship in the undiseased adult population.Multimodal clinical data from the UK Biobank, primarily cardiac MRIs and 12-lead ECGs, was used to generate patient-specific biventricular geometry and vectorcardiograms.Five alternative definitions for the 3D orientation axes of the electrical and anatomical axes were computed, followed by assessment of their mutual alignment.Findings demonstrate that maximal alignment occurs between the anatomical axis derived from the vector connecting the valvular plane centre to the apex, and the electrical axis defined by the maximum QRS dipole magnitude in the vectorcardiogram.Furthermore, the electrical axis orientation displays a wider spread than that of the anatomical axis and has a dominant effect on the coupled axis interplay.